1. Field of the Invention
The present invention relates to a semiconductor memory device, and particularly to a semiconductor memory device having a terminal combining an input terminal for address and an input/output terminal for data.
2. Description of Related Art
A semiconductor device is mounted to a cellular phone or the like. In a cellular phone or the like, data is transferred between a semiconductor memory device (hereinafter referred to as a memory) and other functional circuits such as CPU (Central Processing Unit). In recent years, the data transfer efficiency is desired to improve. One of the methods for the improvement in data transfer efficiency is to increase the number of buses connecting between the memory and CPU etc. This method increases the amount of data that can be transferred in one access by increasing the number of buses. On the other hand, in mobile devices such as a cellular phone provided with a memory, a package of a semiconductor device is desired to be miniaturized. An increase in the number of buses increases the number of pins formed in a memory. The increase in the number of pins is detrimental to the miniaturization of a memory.
Therefore, Japanese Unexamined Patent Application Publication No. 11-328971 (Choi) discloses to use the same pins for inputting/outputting a data signal and inputting an address signal.
The technique set forth by Choi discloses to input/output data through a pin for inputting addresses by inputting a particular control signal. However, the technique only discloses that a memory disclosed by Choi inputs/outputs data through a pin for address. Control of addresses for inputting and input of command to the memory are not taken into consideration for the memory disclosed by Choi. Moreover, Choi only discloses to switch an input of an address pin for an asynchronous memory.
On the other hand, there are memories in recent years that have a burst mode as in a synchronous DRAM (Dynamic Random Access Memory). In the burst mode, a memory carries out a specific operation when accessing the memory with different burst length or inputting a command to the memory.
When using an address terminal for inputting/outputting data in an asynchronous memory as the one disclosed by Choi, detailed access operations and command inputs to an address as in a SDRAM are not possible. On the other hand, in order to transfer a huge amount of data at a time, there has been a case where the number of pins for data input/output terminal is limited by an address terminal and a terminal for command input in a SDRAM or the like.
The present inventor has recognized that in the semiconductor memory device disclosed by Choi, if sharing a pin used for data input/output with an address pin, addresses and commands cannot be input through the address pin, thereby reducing the data transfer efficiency.